School of GeographyFACULTY OF ENVIRONMENT

Working with Tables

Viewing Attribute Data

• attribute data are organised in database tables

ArcMap

• Right click a data layer in the data frame

• Open Attribute Table

OR create a report or graph

ArcCatalog

• Click on a layer and preview the table

Table Window

• Rows (Records) + Columns (Fields)

• Features or standalone table

• Dynamic contents – move fields, change fonts, freeze

Columns (Fields)Rows (Records)

Unique

ID

Tabular Data Field Types

• Different field types store different kinds of values

• Choose the right field type for the right value

• Field types vary according to table format

• Text, date, short, long, BLOB (graphics), double

• CNTRY_NAME: Russia – text

• POP_CNTRY: 151,827,600 – long

• COLOR_MAP: 3 – short

• SHAPE_AREA: 321294461992.126 – double

• Layer Properties Field tab

Navigating Tables

• Show All or Show Selected features

• Highlight records within show selected view

Show selected and show all views

Navigate rows

Table Window Menus

Menus for row, columns and cells – right-click

Options Menu

Options menu is drop down

Row Context Menu - Identify

ArcToolbox

• Access this through the ArcToolbox icon:

• Contains a variety of geoprocessing tools

• Functions in ArcToolbox can sometimes be carried out in context menus (right-clicking)

• Extensions will also appear

• Will be looking at some of the Analysis Tools tomorrow

Creating A New Field

• Suppose you want to calculate a value in a table based on existing data

• Need to add a new field

• Can add a field through the Data Management Tool

• Can add a new field through the Options menu in the table

Calculations in a New Field

• Can do this either through ArcToolbox or the Column Context Menu (right-click on column name)

• Both present you with a Field Calculator

• Can also delete the field if you are not happy with it = permanent!

Editing Data in the Table

• Enable the Editing Toolbar (View Toolbars Editor)

• Open the attribute table you want to edit

• Start Editing – headings of the table will go white

• Make changes

• Stop Editing and choose whether you want to save

Working with Tables

Hands-on Exercise #5

Basic Statistics on a Field

• You can generate basic statistics on any field in the table

• Click on the name and right-click to select Statistics

• Does NOT work on text fields

Statistics Summary

• Can move between fields using the drop down box

• Will only see fields that are numerical

Statistics on a Selection

Summarise by a Field

• Might want to sum up occurrences of an event in an area

• Might want to find out the min or max value of an event in an area

• E.g. summarise the number of pupils by LEA

Calculations with Tables

Hands-on Exercise #6

Mapping Spatial Data from External Sources

• Added by user with editing tools (tomorrow)

• Postcode data

• convert to Easting, Northing

• Data from a GPS receiver

• Depends on the GPS, e.g. the GPS might come with a facility to export a route to a shapefile

• Excellent source of information:

http://www.ordnancesurvey.co.uk/oswebsite/gps/

Bringing Data into ArcMap

• Can load Excel files directly into ArcGIS

• Use the Add Data button and select the sheet where the data are located (sheets are given a $)

• Excel files are read only and can only be viewed

• Need to conform to basic conventions:

• One header line

• No spaces in header names

• Do not start headers with a number

• Don’t format cells as %

• KISS principle

One Line Header

No extra data over here

How to Map the Data - Points

• Geocode your data – turn your postcodes into X,Y coordinates

• Put these values into Excel – two columns with a single header

• For version 9.1, create a .csv, .txt or .dbf file

• Create X,Y data for points

• Tools Add X,Y Data

Mapping Attribute Data from Another Table

• Target table (map) + Source table (which you want to map)

• Joins

• 1 to 1

• Many to 1

• Relates

• Above plus: 1 to Many + Many to Many

• Relationship Classes

Example of a Relational Database

Attribute Join

• Physical connection between two tables

• Appends the attributes of the two tables

• Assumes a 1-to-1 or many[target]-to-1 relationship

Attribute Join Options

• Keep all rows – defaults

• Keep only matching rows

Connecting Tables with Relates

• Defines relationship between two tables

• Tables remain independent

• Can also have 1-to-many and many-to-many relationships

• Make selection and then open related table

• Discovers any related rows

Relate vs Relationship Class

• Relate

• Across different database tables

• Created on the fly in ArcMap, saved in .MXD and .LYR files

• Relationship Class (managed by the geodatabase)

• Permanent relate

• Within the same geodatabase

• Only exists in a geodatabase

Steps on How to Map the Data

• Join the data to a map file so that you can plot it

• Create the file in Excel (and export to .dbf, .csv or .txt if 9.1)

• Follow these basic rules:

• Have a single line header, one name per column

• Avoid spaces or strange characters in the header line

• Avoid formatting as percentages

• Avoid having any extra data outside of the rows and columns of your data

• Avoid starting headings with a number

Steps on How to Map the Data

• In ArcMap, open the file to which you want to add the data

• You can open the .dbf/.csv/.txt file in ArcMap or browse

• Right-click on the layer Joins and Relates

• Choose the column for joining on from the map file that matches the one in the .dbf/.csv/.txt file

• Select or browse for the .dbf/.csv/.txt file

• Select the column in the .dbf/.csv/.txt file that is in common with the map file and then join

• Save the map if you want the join to become permanent (right-click Data Export Data)

Troubleshooting

• <Null> values – can occur if there are features in the map that did not occur in your .dbf/.csv/.txt file – become 0 when join is made permanent

• <Null> values across the board – join was not successful

• Check that you have chosen the correct columns on which to do the join

• Make sure there are no spaces in the name/ids in one column but not the other (hidden spaces)

Bringing Data into ArcMap

Hands-on Exercise #7